The use of portable communication systems has been in existence for decades and the most basic version of such communication system consists of a two-way radio having a receiving circuit and a transmitting circuit incorporated therein. The basic type of two-way radio has been and continues to be used extensively by police forces, firefighters, construction workers, and various other environments. Such basic two-way radio communication systems usually consist of a unit which may be attached to an article of clothing and which is adapted to automatically receive any signals transmitted thereto, amplify the signals and condition the signals to be heard without detaching the unit from the article of clothing.
Generally speaking, these basic types of unit incorporate a manually-operable switch that is capable of converting the unit from a receiver unit to a transmitter unit which is usually designed such that the switch must be manually held in position during transmission of the signal. While such units have received a remarkable degree of acceptance in various fields and are capable of being mass produced at an extremely low cost, certain inherent deficiencies make such units unacceptable in numerous environments.
For example, two-way communication systems are absolutely essential around airports where ground personnel must communicate with aircraft operators for various reasons, such as communication between the ground crew and the pilot while the pilot is taxiing along the runway towards a gate. In such type of environment and many others, it is impossible for the ground crew to be able to utilize the simplified version of two-way radio because of the surrounding noise level. Furthermore, in such environment for safety and health reasons, it is mandatory that the ground crew have headsets on at all times to protect the ears from any sudden dangerous noise level which could result in permanent damage to the ear.
Thus, more recently, two-way communication systems have been developed that are incorporated into headsets or other protective gear, such as helmets, that are worn by various types of personnel, such as aircraft ground crews, construction workers, factory workers, and others. The basic type of two-way communication system incorporated into headsets or other protective devices originally incorporated communicaton and receving units that again had to be manually switched between the "transmit" mode and the "receive" mode by the user. Such operation is not only time consuming and annoying to the user, but could become a safety hazard in the unlikely event that the user neglects to place his equipment in the "receive" mode, and it becomes essential that a transmission be received.
Extensive strides have been made in recent years towards perfection of the two-way communication system wherein the switching between the "transmit" and the "receive" mode is voice-controlled. Such a system, particularly when incorporated into headsets or other type of protective devices, leaves the user free to perform other chores with his hands while communicating through the system. Examples of such types of voice-controlled, two-way communication systems are disclosed in U.S. Pat. No. 4,166,978, incorporated herein by reference, and the various U.S. patents cited therein. Such system as the one disclosed in the above patent, assigned to the Assignee of the present invention, has received a remarkable degree of commercial acceptance since the voice-controlled system incorporates rapid-response switching systems that quickly convert the system between the "transmit" and the "receive" modes whenever there is any interruption in the speech from the transmittor.
While remarkable strides have been made to substantially completely isolate the user of such communication systems from any external sounds, regardless of the noise level in the operating environment, it many times becomes necessary for the user to be able to hear sounds from a fellow worker in close proximity. While numerous systems have been developed, the extremely sensitive systems which are totally soundproof to the wearer from external noises still requires the user to manually separate the headset from the ear a sufficient distance to allow sounds or voices from a fellow worker in close proximity thereto to be heard. Such a procedure is not only cumbersome for the user, but can also cause injury to the ear in the unlikely event that an extremely loud sound rapidly emanates from a source while the user has the headset at least partially removed from the ear, which may cause permanent damage to the ear.
Thus, there remains a need for a simplified type of two-way communication system which normally isolates the wearer from any surrounding sounds that are not transmitted through the communication system itself, but still allows the wearer to easily convert the communication system to a condition where an adjacent worker's voice can easily be heard.